Converting files to DVD player format

I'm converting and burning some files (mkv, avi) to play on a DVD player that accepts "DVD format" only. I've been using Any Video Converter and Free Studio, and while I can make the conversions, I have the following questions/problems:

- When I'm putting two videos on a DVD, what's needed so that they show up separately on the player disc menu?

- Subtitles:
With a file that has hardcoded English, how do I get the converter to recognize the subs? With AVC I've tried Eng 1, Eng 2 and None, all w/o success. I also have a separate sub file that can be used, but it doesn't grab that either when I make the names the same.

- Format: So far I'm being shown the NTSC DVD format of 720x480 only, which renders black bars top and bottom, even though the original files (e.g., mkv, avi) are 1280x720 and play full screen. Anything I can do about that?